B. <em>Today's farm machines can milk more than 100 cows an hour. </em>This is the correct option.
The last sentence refers to the fact that the milking process has become better , today. Therefore, the author will probably write about the effective use of the milking machines. The more cows that can be milked with the farm machines , the more effective the machines will be.
These options are not right:
A. Refrigeration started in 1880, making milk more available. The author is not writing about refrigerating machines but milking machines. The focus is on today's machines , not on the XIX machines.
C. The majority of farms today are still owned and run by families. The author does not mention who owns farms. The focus is on milking machines, not on the owners of the farms.
D. "We've had a dairy cow for years," local farmer Pat Cooper said. This quotation does not reinforce the effectivness of milking machines.